Download Building A D-Star Hotspot at KV5V

Building A D-Star Hotspot at KV5V
Our QTH is located 15 miles from the KE5RCS repeater and on the opposite sides of several
low, rolling hills. Hand-held coverage is spotty here, and there are gaps in the mobile
coverage to the north and around Salado, our nearest town. A Hotspot could eliminate these
coverage problems. It could also make D-Star reflectors, which I enjoy using, available
without forcing the rest of the local repeater users to hear them too. In August, when
Moencomm advertised the Matrix Circuits Star*Board, I decided to build a Hotspot. This
report relates some of what I learned in the process, and it offers some thoughts about the
place of the Hotspot in the D-Star world.
What is a Hotspot?
The term “Hotspot” is used in several radio services to describe areas in which service from a
distant source is improved by installing a local transmitter or receiver. FM stations improve
coverage in mountainous areas by installing local, low-power transmitters. Cell service
providers install hotspots in shopping malls, airports, and homes where normal cell tower
coverage is poor. These are also called Microcells and Femtocells.
In ham radio, a Hotspot is a kind of repeater, made up of an Internet-connected computer, an
interface board called a Node Adapter, and an FM transceiver and antenna. Most important,
it is a “transparent” entry point into the D-Star network. Hotspot users can access D-Star
features as if they were entering the network directly through a repeater.
The computer is connected to the Internet so that, with special software, it can communicate
with the D-Star network. To extend the coverage of our KE5RCS repeater, the KV5V Hotspot
is connected to the repeater Gateway computer and appears to the repeater controller as if it
were a local user entering the system through one of the radios.
It's interesting that even if you don't own one of the expensive ID-1 radios, you can still
communicate with friends on a 23cm Mode A repeater. If the local Mode B and Mode C (3/4m
and 2m) repeaters were busy, a user could enter the Mode A machine through the Gateway
and use it for the QSO. Your conversation would be broadcast on the 23cm frequency, and
as Hotspot users, neither of you would hear it. But you would be using the D-Star system to
communicate over distances too great for simplex operation. (Callsign routing is not possible
with the Dutch*Star software I chose to install.) There is much more to be said about this
“feature” of the Hotspot, but this belongs in another discussion.
The Hotspot software can also connect to Reflectors, using the Dplus Reflector Server and
software which has been added to most repeater Gateways.
The KV5V Hotspot computer and radio.
The Node Adapter connects to the PC through a USB port. It is a small printed wiring board
which contains a microprocessor, a GMSK modem, and some analog and digital interface
components. “GMSK” means Gaussian Minimum Shift Keying, which is part of the electrical
protocol used in many digital radio systems, including cellular systems. In this case, the
GMSK modem prepares the purely digital data received from the D-Star network so that it can
be transmitted by the analog FM radio. It also “massages” the incoming analog signal from
the radio to make it suitable for delivery to the D-Star network.
I chose to use the Star*Board, which is manufactured by Matrix Circuits, LLC in New London,
Iowa. Although it differs mechanically, this board is electrically similar to the Dutch*Star MiniHotSpot available from Fred van Kempen, PA4YBR. Because it is compatible with the MiniHotSPot, the Star*Board can also run Fred's Dutch*Star software.
There's an important distinction to make here. The GMSK modem is not an AMBE vocoder.
In other words, it doesn't compress digitized speech so that it can be transmitted at a lower bit
rate. Nor does it expand compressed digital data to make it sound like speech transmitted
Side view of the computer, showing the Matrix Circuits Star*Board
(Node Adapter) mounted inside, near the rear of the enclosure.
over a 15 kHz-wide FM channel. (The AMBE vocoder, designed by Digital Voice Systems,
Inc., squeezes narrowband FM-quality speech into a 6.25 kHz channel.)
The fact that the Node Adapter contains a modem instead of a vocoder also means that the
voice encoding and decoding must be done by an AMBE chip in the radio which
communicates with the Hotspot. You cannot, in other words, talk to a Hotspot with an FM
transceiver. You must use a D-Star radio such as an IC-92AD, an ID-880, or an ID-2820, all
of which contain AMBE vocoder chips.
The FM radio used with the Hotspot must have a high-speed data port. Most VHF and UHF
radios manufactured in the last ten years or so have 1200 bps and 9600 bps data ports.
These were intended to be connected to Packet controllers. Although the 1200 bps ports
cannot be used with D-Star, the 9600 bps ports can usually be made to support a Node
Adapter. Even older radios, which don't have data ports, can be modified and pressed into
service for D-Star if they are properly modified.
The radio in the KV5V Hotspot is a Yaesu FT-2600M, and the 9600 bps transmit and receive
connections are available at a 9-pin D-sub connector on the rear panel. Although the radio is
capable of 60 Watts of power output, I have set the output to 5 Watts. The output stages in
most mobile radios operate at less than 50% efficiency, so the PA must run at 120 Watts
inputto produce 60 Watts output. The 60 Watts which isn't delivered as RF is dissipated as
heat, which makes the radio become very hot. Efficiency is even poorer at lower output
levels, so as you can see in the photos, I've mounted the radio upside down to make the heat
sink face up. A 120mm computer fan is suspended above the heat sink by brackets. Running
The transceiver sits upside-down on rubber feet so that a 120 mm
computer fan can be mounted on brackets above the heat sink.
at its lowest speed, it keeps the radio heat sink temperature below 100°F.
How Well Does it Work?
With a dual-band colinear antenna mounted about fifteen feet above ground, the Hotspot
coverage area is about five miles in our hilly terrain. Under line-of-sight conditions, it's
useable at ten to fifteen miles. This more than meets my original objective—to improve
repeater coverage in the area around the house and in town.
Increasing the Hotspot transmitter power does little to improve coverage. The main limitation
is the transmit power of the D-Star radio which talks to the Hotspot. A 50 Watt mobile radio
can use the Hotspot at about the same range that it can reliably copy signals from it.
I have also found that, even at their low-power settings, my IC-91AD and the FT-2600M can
easily overload each other when I operate in or around the house. The symptoms are lost
data, which appears as garbled text messages, and “R2D2” (out of synch) speech. So
running higher power doesn't offer any advantages in my installation.
Loss of synch symptoms seem to appear more often when using the Hotspot than when
directly using the repeater. It can also take longer to recover sync with the Hotspot than it
does with the repeater. This may happen for any of several reasons. On one hand, signal
levels on the connections between the GMSK board and the radio may need more
adjustment. I have worked with these, and I believe the transmit level is in the “sweet” spot.
But there may be room for improvement.
Also, although the radio has a 9600 bps data port, it may not be capable of transmitting data
accurately at that speed. Substituting my Ft-817, which also has a 9600 bps port, might tell
me if the radio is at fault. That test will come later.
Finally, I have read suggestions that the DutchStar software is due for updates because it
does not send synch information as often as the ICOM repeater software does. If true, this
would account for the added time it takes for radios to restore synchronization after it's lost.
The complete Hotspot computer and radio.
Some Comments
This section is for those who want to know more about bringing up a Hotspot. It is far from a
complete treatment, but it will highlight some important questions and refer you to sources
which treat the questions more thoroughly.
Bringing up a Hotspot node is not as easy as putting a new radio on the air. When you open
the Star*Board shipping box, you find a small, 2” x 2 5/8” PWB with USB and DB-9
connectors, five headers, where you will install jumpers, and three potentiometers. The USB
A-to-B cable is an over-the-counter item at computer stores. As for the dB-9 cable, you'll
either have to build one or remember to order one when you purchase the node adapter from
Moencomm.
After mounting the Star*Board in or on your computer and connecting the cables, you'll have
to download software from at least two places: The price of the board includes a license to
download Fred van Kempen's (PA4YBR) Dutch*Star software. This is uploaded to the node
adapter board. (Jim Moen will offer to install this software before he ships the board.) Then,
you'll need to download applications which run on the PC, enabling it to operate as a Hotspot
or as a repeater. Although there are several other options, most people appear to be using
the DVAR Hotspot software written by Mark McGregor, KB9KHM.
The downloads will also include a suite of applications, some of which enable you to install
drivers and configure and test the hardware before you bring up the Hotspot itself. Other
applications implement the Hotspot, decode D-Star data, find reflectors, record and play DV
files, etc.
NAWinTEST, for example, has an Echo Test feature which records speech transmitted to the
Hotspot and then plays it back to you on the Hotspot frequency. It also has an RF I/O Read
feature which displays your transceiver configuration information and then serially displays
the D-Star-formatted packets of data transmitted by your radio. This will be a handy tool if
you're interested in learning about the internals of the D-Star system.
If you're beginning to think there are a lot of variables to deal with, you're right. Some
newbies (include me in this group) have problems, but fortunately, Moencomm supplies good
documentation with the board. If you read and follow this carefully, you will probably succeed
without needing more help. If you should need help, you'll have access to lots of it on the
reflector at yahoogroups.com: gmsk_dv_node.
There are many URLs to visit for information about Hotspots. Here are some to get you
started:
www.k6jm.com/dstar.htm – Jim Moen's site at which you will find much more information
about building and running a Hotspot.
www.moencomm.com – The Moencom site, at which you can download information, including
a user manual, about the Star*Board.
http://www.moencomm.com/orders.asp – You can order a Star*Board here.
Http://www.dutch-star.hl/ - Fred van Kempen's site, where he describes his Mini-HotSpot
board. You will also download the DutchStar software for your Moencomm board from this
site.
www.w9arp.com/hotspot/
http://gmskhotspot.com/
Since the KV5V Hotspot often runs continuously for many hours, I have been interested in
reducing power consumption. Initially, I used a netbook to control the node adapter. This
worked well and showed that a single-core, Intel Atom processor had more than enough
horsepower to support the adapter.
Although I could have run the Hotspot on the desktop computer in my shack, I chose to build
a new system, using an ITX (6-inch by 6-inch) motherboard and a compact enclosure. The
Gigabyte GA-D525TUD MB fit nicely in an Apex MI-008 enclosure. The 220 Watt Allied
power supply which is shipped in this enclosure can deliver 16 Amps on its 12 Volt buss, and
the CPU fan is normally the only 12 Volt load it would see. So I chose to use the rest of the
available 12 Volt power to operate the FT-2600M transceiver. It easily runs at up to 10 Watts
output with the computer supply. Twelve Volt cables for the transceiver and fan were routed
through ventilation holes in the rear of the enclosure.
In addition to the Node Adapter, I installed an old 80 GB hard drive and a CD ROM drive. The
power consumption of the computer (without display) is roughly 38 Watts. To reduce this, I
replaced the hard drive (rotating type) with an 8 GB solid-state drive. Power consumption fell
only two Watts, so I had to choose between running the system with the highly reliable SSD
and using the rotating drive, which offered more storage space and allowed me to
occasionally use the system for other purposes.
I chose to go back to the rotating drive so that the computer could also be used with a DV
Dongle and other D-Star applications. I should add that the small APC UPS, which keeps the
Hotspot running during power dropouts, adds ten Watts to the system power consumption.
The choice of operating frequency can be important in some areas. Any two-meter frequency
not occupied by a nearby repeater or regular simplex users would have been acceptable in
my rural location. The Texas VHF FM Society only coordinates repeater pair assignments, so
I was free to choose a frequency myself. Most coordination groups prefer to deal only with
repeater frequencies, so it will be interesting to see what happens when D-Star users begin
setting up Hotspots in urban areas. Even if they limit coverage, there are bound to be
conflicts.
I chose to park the KV5V Hotspot on 145.70 MHz. This seemed appropriate because the
frequency lies in the “Miscellaneous and Experimental Modes” portion of the band. It will be
interesting to see how other users approach this question.
What does the growth of Hotspot technolgy tell us about D-Star? When ICOM demonstrated
that good quality speech could be transmitted in a 6.25 kHz bandwidth using AMBE encoders,
the D-Star system which followed was seen as a new and better way to use our bands for
speech and data communication. The D-Star protocol, however, can support much more.
Regarding Transmitted D-Star Bandwidth: Jim Moen reports that George, KJ6VU, has
examined the signals transmitted by a number of ICOM radios and found that most
have occupied bandwidths of 9 to 10 kHz. Since most Hotspots will be set up without
test equipment, signals from some will be even wider. D-Star only requires 6.25 kHz,
so if you have access to equipment which can measure bandwidth or deviation, you
should use it when you set up your Hotspot.
D-Star simply uses the Internet to transport data, and does addressing using ham radio call
signs. It includes “post offices” (servers) which handle addressing and allow messages to be
directed to specific individuals or broadcast to many users at once. It doesn't discriminate
between voice or pictures or software or any other kind of digital data.
While it's helpful to have the Internet for moving data, D-Star can also function without it.
Local voice and data contacts are possible with the the Internet and Gateway disconnected.
With the Internet unavailable, you can leave the Gateway and router in place and add another
computer with appropriate software. Now, you can have a store-and-forward “local area
network” with a range of 50 miles. Data rates will be slow if you run DRATS on the data
channel of the DV systems. The coverage area will be somewhat smaller if you use the 23
cm DD channel, but you will see real data rates approaching 70 kbps. (We have used the
KE5RCS mode A DV and DD repeaters at 20-25 miles.) This is slow compared with
commercial speeds, but we must remember that D-Star can service remote areas under
conditions that commercial operators find too difficult or uneconomical.
Where does all this lead? For reasons probably best understood by people in the industry,
Kenwood, Yaesu, and Alinco have so far declined to support D-Star with products of their
own. This has made ICOM the sole supplier of D-Star transceivers—a situation which has put
off some potential users. (There are rumors that at least one relatively new Ham Radio
equipment manufacturer is considering building a D-Star radio.)
Keeping with tradition, hams have not allowed the commercial manufacturers to become their
sole sources of equipment. The Hotspot technology, originally developed by Satoshi Yasuda,
7M3TJZ/AD6GZ, has been replicated and expanded by individuals and groups in Europe and
the USA. The DV Dongle, designed by Robin Cutshaw, AA4RC, and Moe Wheatley, AE4JY,
allows users to access the D-Star network while sitting at their computers. No radio is
necessary. Several home-grown D-Star repeater architectures have also surfaced in the last
two years.
What is important is that the D-Star protocol is in the public domain, and it is easily
understood by hams with network training and experience. The digital and RF portions of the
technology offer no new challenges to hams with that kind of design experience. So users
can expect to see D-Star applied in ways that none of us anticipates now.
Brad Rehm
KV5V
Salado, Texas
November 29, 2011